That's a little bit weird but is your internet still working? I remember when I lost my internet connection only the power light was solid then others were flashing. I was informed that the lights on the Arris box should be solid and green. Have you tried turning off and on the box? If yes and still the internet is not working, better to call TPG support as they can assist you further on this issue and for them to check if NBN has faults on the network. But if the internet is still working and the light is still yellow, then it's up to you if you still want TPG to check it.

Hey @lancelot999, thanks for the reply! It doesn't seem to be affecting the internet connection funnily enough. But after a year of only green lights on my NTD I thought it was strange to have an orange light.